Conventional wafer carrier systems bond a process wafer, which may also be characterized as a device wafer, to a carrier for back side processing including substantial thinning of the process wafer, after which the process wafer and carrier are separated. However, in order to sufficiently planarize, as well as thin, a device wafer as bonded to the carrier, the carrier itself when bonded to the device wafer and during the device wafer thinning process, should exhibit a sufficient planarity so as to act as a reference plane and prevent unacceptable deviations from planarity of the thinned device wafer.
While carriers in the form of both semiconductor and glass materials are known, it is currently preferred to planarize semiconductor (generally silicon) carriers in the form of carrier wafers, after bonding to the device wafer and before the device wafer is thinned. This preference is largely due to the ability to use the same equipment to planarize a semiconductor carrier wafer as may be subsequently used to thin and planarize the device wafer. In contrast, due to the different material characteristics of a glass carrier, different equipment and specifically the tool element used to contact the glass, must be employed to planarize a glass carrier.
A significant drawback, however, in the use of a carrier wafer of either a semiconductor or a glass material is the required thinning of the carrier wafer during planarizing thereof. Such thinning, typically of at least about 20 μm to no more than about 30 μm restricts the re-use of the carrier to a relative small number of times before the structural rigidity of the thinned carrier wafer is insufficient to support the device wafer during processing. At such point, the carrier wafer must be discarded and replaced with another carrier wafer. As a result, the high volume of device wafers processed in a modern, state of the art semiconductor fab results in costs of hundreds of thousands of dollars, if not more, per year for carrier wafers.